GULF OF MEXICO - The mobile offshore drilling unit Q4000 holds position directly over the damaged Deepwater Horizon blowout preventeras crews work to plug the wellhead using a technique known as "topkill," May 26, 2010. The procedure is intended to stem the flow of oil and gas and ultimately kill the well by injecting heavy drilling fluids through the blow out preventer on the seabed, down into the well. (USCG) 10Spill0526-G-7444G-016
